1,721,003 research outputs found
Industrial Wastes and By-Products as Raw Feed in the Manufacture of Ordinary or Special Cements
No full textA Porosimetric Study of Calcium Sulfoaluminate Cement Pastes Cured at Early Ages
No full textCalcium sulfoaluminate and Portland cement pastes, both prepared with a water/solid mass ratio equal to 0.5 and cured for time periods comprised between 2 h and 28 days, show completely different pore size distributions by mercury intrusion. Portland cement pastes aged at 12 h and 1 day exhibit a unimodal distribution of pore sizes related to a continuous network of capillary pores with a threshold pore radius decreasing from nearly 650 to 350 nm. After 7 and 28 days of curing, this parameter shifts to about 150 nm and a region having smaller pores appears (with a second threshold pore radius roughly comprised between 10 and 30 nm), made discontinuous by blockages of hydration products which occlude the interconnected pore system and isolate the interior space. For calcium sulfoaluminate cement pastes, a bimodal distribution is rapidly established, in which the regions with a lower porosity (threshold pore radii up to about 25 nm) are dominant, while the decrease of total porosity almost ceases at later ages. The porosimetric behaviour of calcium sulfoaluminate-based cement is related to its very fast hydration rate and to the lack of water needed to continue the hydration reactions
Fluidized bed combustion wastes as a potential source of ettringite for recycling purposes - a hydration study
No full textThe fluidized bed combustion (FBC) technology is very effective in the conversion of solid fuels ensuring also a low environmental impact. A major problem related to the fluidized bed technology is the disposal and/or the utilization of solid wastes, owing to their remarkable quantity and poor quality. In order to find suitable applications fields of these residues, in this work it is explored the possibility of converting them, upon a controlled hydration treatment, into ettringite (6CaO•Al2O3•3SO3•32H2O), a compound having several useful properties. Three types of FBC wastes generated in industrial plants were investigated: 1) FA-Sul, a sulpho-calcic fly ash; 2) FA-Sil, a silico-aluminous fly ash; 3) BA, a sulpho-calcic bed ash. FA-Sul and two binary mixtures (83% FA-Sul/17% FA-Sil and 64% BA/36% FA-Sil) were the most promising, in terms of potential ettringite generation. Hydration tests were conducted at 70°C for 1, 2 and 4 days. Both ettringite and calcium hydroxide (Ca(OH)2) were detected within the hydrated systems, the former being the main reaction product. The kinetics of ettringite formation is related to the sample chemical composition and the conversion degree at 4 days of curing is equal to ~1 for FA-Sul, 0.74 for FA-Sul/FA-Sil and 0.42 for BA/FA-Sil
Sustainable development of the cement industry and manufacture of binders with a reduced environmental impact
No full textUse of atmospheric fluidised bed combustion and desulphurisation residues for the manufacture of non traditional binders.
No full textUtilization of Industrial Wastes and By-Products as Raw Materials for the Manufacture of Portland Cement Clinker
No full text
IMPIEGO DI RIFIUTI INDUSTRIALI IN TOTALE SOSTITUZIONE DELLA BAUXITE COME MATERIE PRIME PER LA PRODUZIONE DI CEMENTI A BASE DI SOLFOALLUMINATO DI CALCIO
No full text
Hydration of coal combustion wastes aimed at obtaining ettringite-based materials
No full textCoal combustion wastes are often used as sources of raw materials, but their utilization degree is still relatively low. Therefore, a greater exploitation in the consolidated fields of use must be pursued and new applications have to be searched for. In view of the manufacture of preformed building elements based on ettringite (a calcium trisulphoaluminate hydrate characterized by good mechanical strength and low density), it has been investigated the hydration behaviour of a sulpho-calcic fly ash generated in an industrial coal combustor. Curing was performed at 70°C up to 4 aging days. X-ray diffraction and thermogravimetric analyses have assessed the fly ash ability to give ettringite as main reaction product within the hydrated system. Calcium hydroxide in the concentration range of about 15-18% was detected. The ettringite amount was comprised between about 43% (1d-curing) and 58% (4d-curing)
- …
